During the manufacture of IC devices including digital logic, an advantageous (but essentially required) approach is to perform some type of manufacturing test in order to prevent faulty devices from reaching the field. The primary goal of such tests is to thoroughly test all paths within each device under normal operating conditions. Unfortunately, such manufacturing test goals are not entirely practical. For example, well-known manufacturing test techniques, such as SCAN and MBIST, can test virtually all of the paths in a device but at a substantially reduced operating rate. These test techniques are problematic, because their reduced operating rates are far removed from the devices' normal operating conditions. Similarly, a manufacturing tester can apply functional vectors to a device, which can confirm a certain percentage of the device's functionality. However, this technique is also problematic, because the tests have to be performed at a reduced clock rate.
One approach currently used to increase manufacturing test coverage is the concept of At Speed Functional Testing (ASFT). The ASFT approach includes an embedded circuit in an IC device, which tests the functionality of the device at its full operating rate. For example, assume that the device to be tested is a device that routes data packets. An ASFT (embedded circuit) for such a device may contain predefined packets that the ASFT applies to the circuits in the device. The ASFT also monitors the output of the device, in order to confirm that the correct packets were routed to the correct destinations.
Notwithstanding the advantages of the existing ASFT approach, as digital signal processing encroaches further into the traditionally analog signal processing fields, such as in Radio Frequency ICs (RFICs), the specific mechanism of ASFT for such signal processing needs to be considered. For example, the data path for the digital logic has become digital values representing an analog signal instead of packets of data or transactions. Thus, the existing challenge for testing in this digitized environment is how to generate “analog” data, check that data, confirm functionality, and achieve a reasonably high coverage rate with the test involved. As such, one option may be to store a sampled waveform in memory, and essentially play that waveform out during the test process. Unfortunately, a substantial amount of memory would be required just to store such a waveform, which would dramatically increase the silicon area required for that device. Therefore, it would be desirable to have a test technique that provides ASFT or a similar approach for testing a digital signal processing chain in an IC device, with an analog broadband signal that toggles a relatively high percentage of the signal processing chain's data path registers, generation of the signal requires relatively little silicon area, and the signal is also repeatable. Such a technique could provide substantial test coverage of the functionality of the device, with a relatively small impact on its silicon area requirements, and tests could be performed at the normal operating speed of the device.